This proposal is based on our studies which have shown a novel interaction between mycoplasmas and lymphocytes. During the infective process mycoplasmas behave as multivalent ligands and cap on the surface of the lymphocyte in the absence of specific antibody. Furthermore, the mycoplasmas behave as potent mitogens and there is a high degree of correlation between capping and blast transformation. Our objective is to analyze the mechanisms of the capping process and their relationship to lymphocyte activation. We shall identify those components of the mycoplasma membranes that cap and activate lymphocytes and also those lymphocyte subpopulations which undergo blastogenesis. A further consequence of the capping process is that the mycoplasma caps are shed from the surface of the lymphocyte as an aggregate containing host membrane material. We intend to establish if these shed caps contain highly enriched mycoplasma receptors and if the capping and shedding of host membrane components leads to antigenic modulation of the lymphocyte surface membrane.